The long term goal is to understand the mechanisms by which chick spinal cord motoneurons form behaviorally appropriate circuits during neural development. Such basic mechanisms play a role in nerve and spinal cord regeneration, and in plastic changes of the nervous system in response to injury. The studies are also relevant to developmental defects of both nerve and muscle. Embryonic surgery and vital staining of identified neurons with fluorescent probes will allow the dynamic behavior of the migratory muscle precursor cells and neuronal growth cones to be documented in cultured slice preparations using time lapse cinematography and video-microscopy. The molecular nature of factors that affect patterned neuronal outgrowth will be assessed by the application of poly and monoclonal antibodies to such slice preparation (i.e. antibodies to NCAM, laminin, etc.). Both polyclonal and monoclonal antibodies will be generated to limb and spinal cord at the stages of initial axonal outgrowth, in an effort to obtain antibodies that block specific growth cone decisions. Finally, the glycogen depletion technique will be used to probe the role of motoneuron cell death and functional activity in refining motor projections within muscles, including the matching of fast and slow motoneurons and muscle fibers.